This application is based on and claims priority of Japanese Patent application No. 2001-369367, filed in the Japan Patent Office on Dec. 3, 2001, the disclosure of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a method of fabricating a rechargeable lithium battery, and a rechargeable lithium battery fabricated by the same.
(b) Description of the Related Art
The demand for rechargeable lithium batteries having a high energy density and a longer cycle-life is increasing as the use of portable electronic instruments such as portable phones, camcorders, and notebook computers increases.
One of the known factors that shortens the cycle-life is decomposition of an electrolyte caused by direct contact between a negative electrode and the electrolyte.
One attempt at preventing such decomposition of the electrolyte involved adding at least one anionic polymerizable monomer to the electrolyte. During charging, the monomer is polymerized to form a polymer layer on the surface of the negative electrode, which prevents the direct contact between the negative electrode and the electrolyte, thereby inhibiting the decomposition of the electrolyte.
However, in order to sufficiently inhibit the decomposition of the electrolyte, an excessively thick layer is required which results in the decrease of conductivity of lithium ions. Such a decreased conductivity deteriorates battery performance factors such as charge and discharge efficiency, high rate discharge characteristics, and low temperature characteristics.
In one embodiment, the invention is directed to a method of fabricating a rechargeable lithium battery. In this method, an electrolyte including a polymerizable monomer is placed between a positive electrode and a negative electrode to prepare an electrode element. The electrode element is pulse charged. The pulse voltage includes a base potential E1 and a pulse potential E2. Herein, the potential refers to a voltage which is proportional to a lithium metal reference electrode potential. The base potential E1 refers to a voltage at which the transfer of electrons from the negative electrode to the polymerizable monomer does not occur, and the pulse potential E2 refers to a voltage at which the transfer of electrons from the negative electrode to the polymerizable monomer occurs.
Alternatively, the electrode element may be further charged at a constant current until the potential of the negative electrode reaches the base potential E1 prior to the pulse charge. Alternatively, the electrode element may be further charged at a constant current (formation step).
Alternatively, the charging step is performed by first pulse-charging wherein the base potential E1 of the negative electrode and the pulse potential E2 are alternated, and by second pulse-charging where a base potential E3 and a pulse potential E4 are alternated.
The charging step may be performed by applying a battery voltage (V1 and V2) corresponding to the potential of the negative electrode rather than the potential which is proportional to the lithium metal reference electrode potential.